This invention relates to controlling emissions from internal combustion engines, such as from fixed-speed engines driving electrical generators and the like.
Reducing combustion engine exhaust emissions is a continual object of research and development, driven both by awareness of environmental effects and increased government regulation. Some of the most effective and cost-efficient emissions controls involve the use of downstream chemical catalysts that further oxygenate incompletely combusted compounds. Sometimes exhaust is directed sequentially through multiple catalyst beds. It is generally understood that higher catalyst temperatures provide more effective emissions control. Much exhaust catalysis development has been focused on developing catalytic converters for automotive applications, in which engine speed varies substantially with vehicle speed and gear selection.
In several other applications, such as in powering fixed-frequency electrical generators, engine speed is held as constant as possible during use, even while generator and engine loads fluctuate. Some engine-generator sets are designed for installation on board moving vehicles, either on land or in water.
Marine generators are subjected to specific regulations, both for emissions and for safety concerns. For example, exposed engine surface temperatures (including exhaust system surface temperatures) must be kept low to avoid increased risk of fire hazard. Seawater is injected into many marine engine exhaust flows so as to cool exiting exhaust gases, and seawater is also frequently circulated through exhaust system components so as to maintain low surface temperatures.
Further improvements in exhaust emissions controls for constant speed engine applications are desired, particularly improvements suitable for marine use.
Many aspects of the invention feature methods of controlling emissions from a fixed-speed internal combustion engine.
In one aspect, the method includes governing engine speed with respect to a selected constant speed; flowing exhaust from the engine through an exhaust system, the exhaust flowing through, in order, a first catalyst, an inter-catalyst space, and a second catalyst; injecting oxygen-laden gas (such as atmospheric air) into the exhaust in the inter-catalyst space, such that the exhaust and the oxygen-laden gas both flow through the second catalyst; and controlling a rate of oxygen-laden gas injection as a function of a variable that changes with engine load.
In some cases, controlling the gas injection rate includes electronically monitoring the variable that varies with engine load. For example, the rate of gas injection may be selected from a specific series of discrete rates as a function of the monitored variable. In some applications the gas injection rate is controlled by an electronic controller with memory configured to store a predetermined table of variable values and associated gas injection rates.
In some preferred embodiments, the engine is driving an electrical generator. In some such embodiments, the monitored variable is generator output current.
In some other embodiments, the monitored variable is engine driveshaft torque or exhaust manifold pressure.
Preferably, the injection rate is increased when engine load increases, and decreased when engine load decreases.
Controlling the gas injection rate includes, in some embodiments, varying operating speed of an air pump motivating the oxygen-laden gas into the inter-catalyst space. In some other embodiments, it includes modulating a valve operably disposed between a source of pressurized oxygen-laden gas and the inter-catalyst space. The valve may be a dump valve, for example, modulated to dump a variable proportion of an incoming flow of gas to atmosphere.
In some instances, water (such as seawater) is injected into the exhaust downstream of the second catalyst. This may be water employed to cool the exhaust housing about the catalysts. For example, the first and second catalysts may both be disposed within a water-jacketed housing, with cooling water flowing through the housing is injected into the exhaust downstream of the second catalyst. In some cases, the first catalyst is disposed within a water-jacketed exhaust manifold and the second catalyst is disposed within a water-jacketed exhaust elbow secured to an outlet of the manifold, with cooling water flowing from the manifold into the elbow before mixing with the exhaust. This arrangement is particularly useful to marine applications with tight exhaust surface temperature requirements and available seawater.
According to another aspect, the method includes governing engine speed to maintain a desired generator output frequency over a range of operating loads; flowing exhaust from the engine through an exhaust system, the exhaust flowing through, in order, a first catalyst, an inter-catalyst space, and a second catalyst; determining approximate engine load; injecting air into the exhaust in the inter-catalyst space at a rate selected according to the determined approximate engine load; and injecting seawater into the exhaust downstream of the second catalyst.
In many preferred embodiments, approximate engine load is determined by monitoring generator output, and wherein in the rate of air injection is selected according to the monitored generator output. The monitored generator output can be, for example, generator current.
In some cases, approximate engine load is determined by monitoring engine exhaust manifold pressure, the rate of air injection being selected according to the monitored manifold pressure.
The first and second catalysts are both preferably disposed within a water-jacketed housing, that may be hydraulically connected to a source of seawater. In some cases cooling water flowing through the housing is injected into the exhaust downstream of the second catalyst.
According to another aspect, the method includes governing engine speed with respect to a selected constant speed; flowing exhaust from the engine through an exhaust system, the exhaust flowing through, in order, a first catalyst, an inter-catalyst space, and a second catalyst; injecting oxygen-laden gas (such as atmospheric air) into the exhaust in the inter-catalyst space, such that the exhaust and the oxygen-laden gas both flow through the second catalyst; and controlling a rate of oxygen-laden gas injection as a function of temperature within the inter-catalyst space.
In a preferred configuration, controlling the gas injection rate includes electronically monitoring inter-catalyst space temperature, and may also include selecting the rate of gas injection from a specific series of discrete rates as a function of inter-catalyst space temperature.
In some cases, the engine is driving an electrical generator.
The gas injection rate is preferably increased when inter-catalyst space temperature increases.
Controlling the gas injection rate may include varying operating speed of an air pump motivating the oxygen-laden gas into the inter-catalyst space, or modulating a valve operably disposed between a source of pressurized oxygen-laden gas and the inter-catalyst space, for example.
In some applications, water (such as seawater) is injected into the exhaust downstream of the second catalyst.
As discussed above, the first and second catalysts are both preferably disposed within a water-jacketed housing for some applications. Cooling water flowing through the housing may be injected into the exhaust downstream of the second catalyst. In one configuration, the first catalyst is disposed within a water-jacketed exhaust manifold, and the second catalyst is disposed within a water-jacketed exhaust elbow secured to an outlet of the manifold, with cooling water flowing from the manifold into the elbow before mixing with the exhaust.
According to yet another aspect, the method includes governing engine speed with respect to a selected constant speed; flowing exhaust from the engine through an exhaust system, the exhaust flowing through, in order, a first catalyst, an inter-catalyst space, and a second catalyst; injecting oxygen-laden gas into the exhaust in the inter-catalyst space, such that the exhaust and the oxygen-laden gas both flow through the second catalyst; sensing carbon monoxide at a point downstream of the second catalyst; and controlling a rate of injection of the oxygen-laden gas as a function of sensed carbon monoxide.
In some embodiments, controlling the rate of injection of the oxygen-laden gas includes varying the rate of injection as a function of a variation of sensed carbon monoxide between different injection rates.
In some configurations, a portion of the exhaust is diverted into an auxiliary flow path downstream of the catalysts, and carbon monoxide is sensed by a sensor disposed along the auxiliary flow path. The diverted portion of exhaust may be passed through a cooler and/or a filter disposed along the auxiliary flow path upstream of the sensor.
According to another aspect of the invention, an engine-generator set includes a fixed-speed internal combustion engine and an electrical generator coupled to an output shaft of the engine. The engine includes an exhaust system containing first and second catalyst beds and defining an inter-catalyst space between the beds, and an air pump connected to the exhaust system to introduce a flow of air into the inter-catalyst space as a function of a variable that changes with engine load.
In many applications, the flow of air is controlled by an electronic controller. The controller is preferably configured to select a rate of gas injection from a specific series of discrete rates as a function of the monitored variable, and may include memory configured to store a predetermined table of variable values and associated gas injection rates.
In some embodiments, the variable is generator output current and the engine-generator set includes a sensor responsive to generator output current. In some other cases, the variable is engine driveshaft torque and the engine-generator set includes a sensor responsive to driveshaft torque.
In yet some other configurations, the variable is exhaust pressure. For example, exhaust manifold pressure may be sensed by a sensor responsive to exhaust manifold pressure, or exhaust backpressure may be sensed by a sensor responsive to exhaust pressure downstream of the catalyst beds.
The air pump may be electrically driven, with speed of the pump controlled as a function of the variable that changes with engine load, or the air pump is driven by the engine, with the flow of air introduced into the inter-catalyst space through a valve that is controlled as a function of the variable that changes with engine load, as examples.
The first and second catalysts may be both disposed within a water-jacketed housing, such as with cooling water flowing through the housing and injected into the exhaust downstream of the second catalyst. For example, the first catalyst may be disposed within a water-jacketed exhaust manifold, and the second catalyst is disposed within a water-jacketed exhaust elbow secured to an outlet of the manifold, with cooling water flowing from the manifold into the elbow before mixing with the exhaust. For marine applications, the water-jacketed housing may be hydraulically connected to a source of seawater. Preferably, the entire inter-catalyst space is disposed within the water-jacketed housing.
For marine power generation, the engine-generator set may be mounted to the hull of a boat for providing on-board electrical power.
According to another aspect, an engine-generator set includes a fixed-speed internal combustion engine and an electrical generator coupled to an output shaft of the engine. The engine includes an exhaust system containing first and second catalyst beds and definse an inter-catalyst space between the beds. An air pump is connected to the exhaust system to introduce a flow of air into the inter-catalyst space as a function of temperature within the inter-catalyst space.
In some embodiments, a temperature sensor (such as a thermistor or thermocouple) is disposed within the inter-catalyst space and spaced from both first and second catalysts. An air flow controller is adapted to receive a signal from the temperature sensor and to vary flow of air into the inter-catalyst space as a function of the received signal.
According to another aspect of the invention, a method of sensing a target component of an exhaust stream includes diverting a proportion of the exhaust stream, cooling and/or filtering the diverted proportion, sensing the target component in the cooled and/or filtered diverted proportion, and then reintroducing the diverted proportion to the exhaust stream at a point downstream of where it was diverted.
In some embodiments, the diverted proportion is reintroduced in a venturi through which an undiverted portion of the exhaust stream flows.
In some cases, the method includes controlling a valve positioned within the exhaust stream between where the diverted proportion is diverted and where it is reintroduced.
In some embodiments, the diverted proportion is cooled by passing through a channel defined within a water-jacketed manifold receiving exhaust from multiple cylinders of an internal combustion engine.
Various aspects of the invention can improve engine emissions by further reducing levels of a selected emissions component, such as carbon monoxide, after the exhaust has flowed through a first catalyst bed optimized for overall emissions reductions. Control of an injected air stream into the exhaust ahead of a second catalyst can be accomplished with feedback from readily monitorable parameters related to engine load, such as generator current or exhaust system pressure, or by temperature of the catalyst or exhaust. Such control can be particularly useful in maintaining efficient catalysis temperatures in systems such as marine engines, where external exhaust temperatures must be kept particularly low, such as by liquid-cooling exhaust components. Some aspects of the invention can be useful for improving the reliability of sensors sensing target components of an exhaust stream, such as CO.
Some of the aspects of the invention may also have utility in controlling emissions from combustion engines in applications in which the engine speed varies significantly.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.